Compressor valve control



Nov. 1, 1938. B. s. AIKMAN 2 COMPRESSOR VALVE CONTROL Filed May 26, 1936 5 Sheets-Sheet 1 INVENTOR HLIRTEIN S- AIRMAN ATTORN EY Nov. 1, 1938. B. s. IAIKMAN 2,135,247

COMPRESSOR VALVE CONTROL Filed May 26, 1956 3 SheetsSheet 2 INVENTOR BURTON S.A|KMAN ATTORN EY Nov. 1, 1938. B. S. AIKMAN COMPRESSOR VALVE CONTROL Filed May 26, 1956 3 Sheets-Sheet 3 I35 I38 IZQ INVENTOR BURTON SAIKMAN Y wm/w ATTORN EY Patented Nov. 1, 1938 UNITED STATES oomansson VALVE comm.

Burton S. Aikman, Wilkinsburg, Pa., assignor to The Westinghouse Air Brake Company, Wilmerding, Pa., a, corporation of Pennsylvania Application May 26,

'1 Claims.

This invention relates to fluid compression apparatus, and more particularly to means for controlling the operation of valves in a fluid compressor or the like.

The principal object of my invention is to provide an improved fluid compressor having an inlet valve actuated by a movable abutment subject to the pressure of the fluid in a chamber, and incorporating means for regulating the supply and release of fluid under pressure to and from this chamber in timed relation to operation of the compressor.

Another object of the invention is to provide means controlled by the pressure of lubricant in a pressure lubricating system of a compressor for positively operating the inlet valve or valves in accordance with the speed of the compressor, so as to effect operation thereof with maximum emciency, and adapted to efiect unloading of the compressor while operating at a speed below a predetermined rate.

A further object of my invention is to provide pressure responsive means controlled by fluid lubricant in the pressurelubricating system of a compressor having one or more fluid compressing pistons, for operating the inlet valves of the compressor, and distributor means operative to control the supply'fluid lubricant under pressure to the pressure responsive means .of each inlet valve so as to effect the operation of said inlet valves in timed relation to the operation oi. the respective pistons and said compressor.

Another object of my invention is to provide an improved fluid compressor.

Other objects of the. invention and novelty will be apparent from the following description, taken in connection with the accompanying drawings, in which:

Fig. 1 is a vertical sectional view of a multicylinder compressor embodying one form of my invention; Fig. 2 is a sectional view taken substantially on the line 22 of Fig. 1; Fig. 3 is a view of a portion of the compressor casing taken substantially on the line 3-3 of Fig. 1; Fig. 4 is a sectional view of the lubricant pump, taken substantially on the line 4-4 of Fig. 1; Fig. 5 is a sectional view of a portion of said lubricant pump taken substantially on the line 5-5 of Fig. 1; Fig. 6 is a reduced sectional view of theline 8-8 of Fig. 7.

Referring to Figs. 1 to 6 of the drawings, one form of the invention is shown associated with a compressor of the multi-cylinder type, which comprises a crank case l containing a fluid lubricant supply or sump ll a cylinder casing I2 features of.

1936, Serial No. 81,861

mounted on the crank case, and a cylinder head l3 secured to said cylinder casing. Contained in suitable bores in the cylinder casing [2 are fluid compressing pistons l6 and II, the piston l6 having at its upper side a compression cham- *ber 18, which is connected with a discharge pipe 20 through a communication controlledby the usual discharge valve 2|, as shown in Fig. 6, which is urged to the seated position by a spring 2la, while the piston I! has associated therewith a similar compression chamber and discharge valve (not shown) controlling communication with said discharge pipe. 1

A crank shaft '22, which may be driven by any suitable. means (notshown) is provided within the crank case It] for operating the pistons. The crank,,shaft has end bearings 23 and 24 journaled in ball bearing assemblies 25 and 26, respectively, which are mounted in the crank case l0, and an intermediate bearing 28 journaled in a ball bearing assembly 29, which is mounted in an interior wall 30 oi-said-crank case, as shown in Fig. 1. Associated with the crank shaft are connecting rods 32 and 33, which are operatively connected in the usual manner to the pistons l6 and I1, respectively, the connecting rod 32 being journaled on a crank pin 35 of the crank shaft, and the connecting rod 33 being journaled on a crank pin 36, said crank pins being spaced about 180 apart.

The cylinder casing 12 has formed thereon at one side of the bores therein valve casing portions 40 and 4i, while the cylinder head l3 has extensions 43 and 44, which respectively correspond to and cap said valve portions. Contained in the casing portion 40 is an inlet valve 46, which is adapted to engage a seat 41 to control communication between a chamber 49, which is connected to the atmosphere by way of a passage 48, as is best shown in Fig. 6 of the drawings, and a chamber 50 above the valve which is connected by way of a port with the chamber 18 above the piston l6.

The inlet valve 46 has a stem 52, which is slidably mounted in a. suitable bore formed in the casing portion 40 and is connected to a piston 53 mounted in a bore in said casing portionand having at one side thereof a chamber 54 and at the other side a chamber 54a. A spring 55 is interposed between the inlet valve 46 and the lower wall of chamber 49 for urgingthe valve away from its seat, the piston 53 being adapted to operate 'said valve according to the pressure of fluid lubricant supplied to the chamber 54 in the manner hereinafter described.

In order to prevent the possible leakage of lubricant past the stem 52 into the chamber 49, said stem is provided with an annular groove 51 connected through a radial bore 58 and central bore 59 to the chamber 540. at the lower side of tlie piston 53, which chamber is connected to the crank case chamber by way of a drain passage 6| formed in the cylinder casing, so that oil leaking past the stem will flow into the groove 51 and thence through the radial bore 58 and the central bore 59 to chamber 54a and will drain,

from said chamber through passage 6| back to the crank case chamber.

Similarly, the casing portion 4| contains an inlet valve 63, which is adapted to engage a seat by way of bores 16 and H with a chamber 33a,

below said piston, which communicats by way of a drain passage 18 with the crank case chamber. r

For supplying fluid lubricant under pressure to the chambers 54 and 13 to operate the inlet valves and to lubricate the compressor, a combined lubricant pumpand distributor device is provided. In the embodiment of my invention now being described, the lubricant pump is of the gear type, and comprises a gear secured to the end of the crank shaft 22 by means of a key 8|, and a gear 83 having an axial stud 84, one end of which is rotatably mounted in a suitable bore inthe crank case Ill, the other end being similarly mounted in a bore in a cover plate 85, which is vsecured to the end face of said crank case by bolts or other means (not shown).

The teeth of the gears 80 and 88 intermesh and are operative in the usual manner to draw lubricant from the supply ll, through an inlet passage 81 communicating with said supply adjacent the lowermost point therein, as is best shown in Figs. 1 and 3, to an inlet chamber 88 in the crank case, and to convey said lubricant to an outlet chamber 89. The outlet chamber is connected by way of a passage 98 with an annular chamber 9| surrounding the crank shaft 22 adjacent to one end, and thence through a passage 93 to the lowermost portion of a reservoir 94. The reservoir 94 is substantially leak tight and is preferably formed in a portion integral with the cylinder casing H.

The crank shaft 22 has a radial bore 96 which communicates with the annular chamber 9|, said bore being connected to a lubricant'duct 91 leading through the crank shaft to a valve chamber 98 formed in a counterweight portion [08. The valve chamber 98 communicates through a passage 99 with the chamber within the crank case l0. Positioned in the valve chamber 98 is a ball valve II, which is adapted to be forced to a seat surrounding the end of the passage 91 by centrifugal force upon rotation of the crank shaft at a predetermined speed, so that when the compressor is operating at a high speed, the valve IOI prevents flow of lubricant from the pump back to the crank case l8, thus permitting the pump to build up a pressure on the lubricant pumped.

In addition the duct 91 in the crank shaft communicates by wayof branch ducts 91a with the bearing surfaces on the crank pins 35 and 38 so as to lubricate these-surfaces.

The gear 89 is constructed and arranged to control the supply and release of lubricant under pressure to and from the chambers 54 and 13 on the faces of the pistons 53 and 12 for operating the inlet valves of the compressor. As shown in the drawings, the gear 80 has an annular cavity M5 formed in the inner face thereof and this cavity is adapted always to register with a port 806 formed in the crank case wall and communicating with the passage 93, while an arcuate cavity 581 is formed in the outer face of the gear 80 and communicates by way of a passage H88 extending through the gear 80 with said annular cavity 905. The arcuate cavity H11 is adapted to register with a port ill in the cover plate during the compression stroke of the piston H, and with a port H2 in said cover plate during the compression stroke of the piston E6, the port ill being connected through a. pipe and passage M3 to the chamber 13 in the valve casing portion ti, and the port H2 being connected through a pipe and passage M4 to thechamber 54 in the casing portion 40.

An arcuate cavity H6 is also formed in the outer face of the gear to and is suitably spaced from the arcuate cavity H11 so as to register with the port til during the suction stroke of the piston l7 and with the port H2 during the suction stroke of the piston 46, this cavity being adapted to establish communication from either of said ports iii and H2 through a passage H1 in the gear 80 and the crank shaft 22, and thence through a passage H8 in the cover plate 85 and crank case it] to the crank case chamber and sump ll.

In operation, the crank shaft 22 is rotated in a. clockwise direction,-as viewed in Fig. 4 of the drawings, and the pistons Ni and I! are thereby operated in the usual manner, one of said pistons moving in its suction stroke while the other moves in its compression stroke. At the same time, the gears 88 and 83 are operated by the crank shaft to draw fluid lubricant from the supply II, through the passage 81 to the inlet chamber 88 and to deliver lubricant from the inlet chamber to the outlet chamber 89, from which lubricant is forced under pressure through the passage 98, cavity 9| and passage 93 to the reservoir 94. The volume of air trapped in the reservoir above the fluid lubricant therein ensures a substantially constant pressure in the lubricating system.

Fluid lubricant is also supplied from the passage 93 through the port I08 to the annular cavity I05 in the gear 88, and flows therefrom through the passage I08 to the arcuate cavity I01. As the gear 80 is rotated by the crank shaft 22 the cavity In! is brought into registration with the port Ill upon each compression stroke of the piston l1 and into registration with the port H2 upon each compression stroke of the piston l6, so that lubricant is forced alternately through said ports into the conduits H3 and H4, charging said conduits and the respective piston chambers 13 and 54 connected thereto.

Lubricant supplied to the chamber 9| also flows by way of the passage in the crank shaft 22 to the lubricant duct 91 therein, from. which it is fed to the bearings by way of the branch ducts 91a.

While the compressor is operated at a speed less than a, predetermined rate, as during the starting period, the lubricant'forced through the lubricant system by operation of the gear pump, as hereinbefore described, is permitted to escape from the duct 9! of the crank shaft past the ball valve IOI to the chamber 98 and thence through the opening 99 to the crank case chamber, thus preventing normal build up of fluid pressure in the system. Consequently, during this period of operation, the pressure of the lubricant acting against the inlet valve pistons 53 and I2 is not sufficient to cause said pistons to close the inlet valves 46 and 63 against the pressures of the springs 55 and I0, respectively, so that the compressor remains unloaded. As the operative speed of the compressor is increased, the ball valve IUI is urged to its seat by centrifugal force and cuts on escape of lubricant from the lubricating system. Thereafter, the pressure in the lubricating system and in the reservoir 94 is rapidly built up by operation of .the gear pump so that the pressure of lubricant is then suflicient to operate the compressor inlet valves.

When the compressor is in the position in which it is shown in Fig. 1 of the drawings, with.

the piston I6 about to operate in its suction stroke and-the piston I1 about to operate in its compression stroke, the cavity III! in the gear 80 is in registration with the port II I, while the cavity H6 in the gear 80 is in registration with the port H2, and lubricant under pressure supplied to the arcuate cavity III! in the gear member 80 in the manner already described is forced therefrom through the port III to the conduit H3 and chamber I3 in the casing portion 4I, thereby operating the piston I2 to move the inlet valve 63 into engagement with the seat 64 and compressing the spring Ill. The piston I1 is then operated to compress air or other fluid in the compression chamber above the piston, the fluid under pressure being discharged past the discharge valve and through the pipe 20.

' Meanwhile, the inlet valve 46 of the other cylinder of the compressor is maintained unseated by the spring 55, which acts through the medium of the valve and stem 52 to force the piston 53 upwardly, since lubricant contained in the chamber 54 and conduit H4 is relieved of fluid pressure as they are connected to the crank case chamber by way of the ports II2, the cavity H6, and the passages II! and H8. On rotation of the crank shaft 22the piston I6 is operated in its suction stroke to draw air or other fluid through 0 the opening 48, the chamber 49, past the open inlet valve 46, to the chamber and through passage 5| into the compression chamber I8.

It will be understood that, as the gears of the lubricant pump are turned when the crank shaft is rotated, the cavities I01 and H6 in the gear 80 are adapted, by reason of their arcuate form, to remain in registration with the ports III and H2 until the piston I6 has substantially completed the suction stroke and the piston II its compression stroke.

As rotation of the crank shaft 22 is then continued, the piston I6 will begin its compression stroke and the piston I! will begin its suction stroke, while the gear 80 is turned to a position in which the cavity I61 no longer communicates with the port III but is in registration with the port H2, and the cavity H6 is moved out of registration with the port H2 and into registration with the port I I I.

When the arcuate cavity I61 registers with the port I I2 lubricant under pressure from the lubricating system flows by way of the pipe III to the chamber 54 and forces the piston 53 downwardly against the opposing force of the spring 55, thereby seating the inlet valve 46.

of the crank shaft.

suction stroke 'of the piston I6 and compression stroke of the piston H, the connections between the arcuate cavity II 6 and port I II and between the arcuate cavity I 0! and port II2 are maintained for a suificient interval to ensure seating of the inlet valve 46 until the piston I6 has substantially completed its compression stroke, while permitting the inlet valve 63 toremain unseated during the suction stroke of the piston I1.

, It will be understood that as operationof the compressor is continued, the cycle of operation as just described is repeated with every revolution In case of failure of the supply of lubricant under pressure, for any cause, the compressor will be automatically unloaded, the inlet valves 46 and 63 being maintained unseated by the springs and I0, respectively.

Means are thus provided for operating the inlet valves of the compressor through the medium of the compressor lubricating system, it being apparent that said means may be adapted for use in a compressor having more than two cylinders by providing the proper ports in a lubricant pressure distributor such as the gear 80.

It will also be apparent that by modifying the exhaust valves of the compressor in accordance with my invention and suitably altering the construction and arrangement of the lubricant pressure distributor, the valve control means could be adapted to operate both the inlet and exhaust valves of said compressor.

Referring to Figs. 7 and 8 of the drawings, there is illustrated a modification of my invention associated with a. compressor of the single cylinder type, which comprises a crank case I20, a cylinder casing I2I and a cylinder head I22, the crank case being closed at one end by a cover plate I23 and containing a lubricant supply I24. The crank case I20 is provided with a cylindrical bearing chamber I25 in which anti-friction bearings I26 are secured for supporting a rotatable shaft I21, which extends through an opening in a closure member I29 secured to the crank case. Any suitable means, such as bolts (not shown), may be provided for securing the several casing sections of the compressor together.

A piston I3I is reciprocably mounted in a bore in the cylinder casing I2I and has at its upper face a chamber I 32, said piston being operable in the usual manner by the shaft I21 through the medium of a connecting rod' I33, which is journaled on a crank pin I34 rigidly keyed to said shaft.

A discharge valve I35 is carried in a valve chamber I36 formed in an extension I31 of the cylinder head I22, said valve having a stem I38 which is guided in a bore in a cap I39 secured to said head and closing the chamber I 36. A spring I46 is interposed between the cap and the discharge valve I 35 for urging said valve toward a seat I4I. v

Disposed in a chamber I 44 formed in an overhanging portion I45 of the cylinder casing I2I is an inlet valve I46, which is adapted to engage Ma, seat I41 for controlling communication from an inlet pipe and chamber I48 and the chamber I44 which is connected with the compression chamber I32 by way of a passage I49.

The inlet valve I46 has a stem I52 which extends through suitable bores in the casing portion I45 and the cylinder casing I2I and into the crank case chamber. The lower end of the stem I52 is provided with a screw-threaded bore into which is screwed the end of the stem I53 of a piston I54, which is mounted to slide in a bore in a member I55 that is secured within the crank case I by means of screws I56, the piston I54 having a pressure chamber I51 at the upper side thereof, while the chamber at the lower side thereof is open to the crank case. A spring I58 is interposed between the outer wall of the member I55 and a spring seat I56 secured to the stem I53, and acts to urge the piston I54, the connected stems I53 and I52, and the inlet valve I46 upwardly, a shoulder I60 on the piston I54 normally engaging the wall of the chamber I51 for limiting upward movement of said elements by the spring I 58.

The spring I58 is thus adapted to bias the inlet valve away from the seat I41, the degree of movement of the valve away from its seat being variable as desired by adjusting the screw-threaded ends of the stem I52 relative to that of the piston stem I53, whfle the stem I52 and the stem I53 may be secured in the adjusted position by tightening the lock nut I6I on the piston stem I53.

A fluid lubricant circulating pump is provided for supplying lubricant under pressure for lubrieating the compressor and for operating the inlet valve' through the medium of the piston I54. As shown in Fig. 7 of the drawings, the lubricant pump comprises a hollow piston I62 pivotally mounted on a crank pin I63, which is formed integral with the crank pin I34. The crank pin I63 is disposed eccentrically relative to the axis of the shaft I21 and is located on the side of this axis opposite the crank pin I34. The hollow piston I62 is adapted to reciprocate within a bore I64 in an oscillating member I65, one end I66 of which is journaled in the cylinder member I55, the opposite end I61 being journaled in a bearing portion I66 that is secured to the crank case I20. The bearing portion I68 has an intake opening I10 which is provided with a screen "I and communicates, through a passage I12 in member I65 containing a ball check valve I13, with'the bore I64 at the lowerside of the hollow piston I 63.

As is best shown in Fig. 8 of the drawings, the passage I12 communicates with a port I15, which registers with an arcuate cavity I16 formed in the cylinder member I 55 adjacent the end bearing I66, and the cavity I16 is connected through a passage I11 with the piston chamber I51.

The hollow piston I62 has a central bore I 18 connecting the bore I64 in the oscillating member I 65 with a lubricant duct I19 formed through the crank pins I34 and I63. A ball valve I80, which is carried in the crank shaft counterweight portion I6I, is arranged to function in the same manner as the check valve IOI shown in Fig. l, to control the pressure of the lubricant in the lubricating system, said valve I80 controlling the flow of lubricant from the duct I19 through the chamber and passage I82. Disposed in the bore I18 of the hollow piston I62 is a ball check valve I84, which is adapted to prevent back flow -of lubricantjrom the bore I18 to the bore I64.

When the crank shaft I21 is rotated, the fluid compressing piston I3I is operated in the usual manner through the medium of the crank pin I34, while the hollow piston I62 is reciprocated within the oscillating member I65 by the crank pin I63. During each suction stroke of the piston I3I, the piston I62 is moved in its upward stroke to draw lubricant from the supply I24 through the screen "I and past the check valve I 13 to the bore I64, the check valve I84 being seated. Upon the compression stroke of the piston I3I, the hollow piston I62 is moved downwardly, so that lubricant is forced from the bore I64 through the passage I12, connected ports I15 and I16 and passage I11 to the chamber I51 lubricant also flows past the check valve I84 in the hollow piston I 62 and thence through the bore I18 and duct I19, excess lubricant being discharged past the valve I80 while the compressor is operating at less than a predetermined speed. So long as the valve I80 remains unseated, the pressure of the lubricant supplied to the piston chamber I51 is insuflicient to move the piston I54 to compress the spring I58, and consequently thereby effects unloading of the compressor.

As the crank shaft I21 is rotated with increased speed, the valve I80 is moved to its seat, so that the subsequent downward strokes of the piston the inlet valve I46 is maintained unseated and I62 are eflective to build up suflicient lubricant placed by the piston I 62 on its downward stroke is substantially in excess of that displaced by the piston I 54, and the lubricant thus forced into the chamber I51 moves the latter piston downwardly against the force of the spring I 58, so as to move the inlet valve I46 into engagement with the seat I41. As the inlet valve is thus moved to its seated position, the piston I 3I is operated to com ess fluid in the chamber I32, the fluid under essure being discharged therefrom by way of the passage I49, chamber I44 and past the discharge valve I35.

Thecompression of fluid in chamber. I32 continues until the piston I3I reaches the upper limit of its stroke, while the pressure of lubricant acting on the piston I54 maintains the inlet valve I46 seated, aided by fluid pressure in the valve chamber I44 acting on the top surface of said valve. on further rotation of the crank shaft the piston I3I is moved downwardly and the hollow piston I62 is moved upwardly, thereby relieving the piston I54 of lubricant pressure I so as to permit the sprin I56 to unseat the inlet valve I46 for again establishing communication from. the inlet chamber I48 to the compression chamber I32.

This cycle of operation takes place on each subsequent-revolution of the crank shaft as operation of the compressor is continued. From the foregoing it will be understood that in the last described embodiment of my invention, the spring I56 is adapted to maintain the inlet valve I46 unseated in case of failure of the lubricant supply, thereby unloading the compressor.

It will thus be seen that the invention provides improved inlet valve means for a compressor of either the single stage or multi-cylinder type, together with means cooperating with a pressure lubricating system to unload the compressor during operation thereof at a low speed, and to effect properly timed operation of said inlet valve means during operation of the compressor at a higher speed.

While two illustrative embodiments of the in-' vention ,'have been described in detail, it is not my intention to limit its scopeto these embodiments or otherwise than by the terms of the appended claims.

Having now described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. In a fluid compressor, in combination, an inlet valve, a pressure lubricating system for said compressor, yielding means for biasing said inlet valve open, pressure actuated means operable for closing said inlet valve, and means associated with said lubricating system and operated according to the speed of the compressor to periodically supply and release lubricant under pressure to and from said pressure actuated means for alternately opening and closing said inlet valve in timed relation tooperation of the compressor. v

2. In a fluid compressor having a plurality of fluid compressing pistons and a crank shaft for operating said pistons; in combination, a pressure,lubricating system for the compressor including a pump; inlet valve mechanisms associated with each of said pistons, each of said mechanisms comprising avalve element, a spring for biasing said valve element open and a movable abutment operative by lubricant at a predetermined pressure for closing said valve element; distributing means operative by the crank shaft for establishing communication from said system sequentially to the movable abutment of each inlet valve mechanism upon the compression stroke of the piston associated therewith; and means for preventing build up of the predetermined pressure in the lubricating system while the compressor is operated, at less than a given speed.

3. In a compressor having one or more fluid compressing pistons and a crank shaft operatively connected thereto, in combination, an inlet valve associated with each piston, liquid pressure operated means for controlling each inlet valve, a gear pump operated by the crank shaft for supplying liquid under pressure to a supply passage and comprising a pair of operatively engaging gears, one of said gears having in one face thereof a first port always communicating with said supply passage and a second port alpiston connected to said stem and subject to the pressure of fluid lubricant in a chamber, means for varying the pressure of lubricant in said chamber for operating the piston to open and close said inlet valve, and means for preannular groove in the stem connected to an interior bore in said stem and communicating through a drain passage with the crank case chamber.

5. The combination with a crank shaft, a cylinder, and a piston slidably mounted in said cylinder and operatively connected to said crank shaft, of an inlet valve controlling the supply of fluid to said cylinder, liquid pressure actuated means for operating said inlet valve, a fluid pressure reservoir, a gear pump' Operated by the crank shaft for supplying liquid under pressure to said reservoir and comprising a pair of operatively engaging gears, one of said gears having in one face thereof a first port always communicating with said reservoir and a second port always communicating with a pressure-relief passage, and a passage communicating with said liquid pressure actuated means and adapted alternately to register for a predetermined time with each of said ports during operation of said gear, wherebyliquid is alternately supplied to and released from said liquid pressure actuated means for operating said inlet valve in timed relation to movement of said piston.

6. The combination with a crankshaft, a cylinder, and a piston slidably mounted in said cylinder and operatively connected to said crankshaft, of an inlet valve controlling the supply of fluid to said cylinder, liquid pressure actuated means for operating said inlet valve, means for maintaining a substantially constant supply of liquid-under pressure in a supply passage, rotary slide valve means operative by said crankshaft and having a supply port always communicating with said supply passage and a relief port always communicating with a pressure release passage, and a passage communicating with said liquid pressure actuated means and adapted alternately to register for a predetermined time with each of said ports during operation of said rotary valve means, whereby liquid is alternately supplied to and released from said liquid pressure actuated means for operating said inlet valve in timed relation to movement of said piston.

7. In a compressor having one or more fluid compressing pistons and a crankshaft operatively connected thereto, in combination, an inlet valve associated with each piston, liquid pressure operated means for controlling the inlet valves, a chamber adapted to contain a liquid, means operative by said crankshaft for pumping liquid under pressure from said chamber to a supply passage, and distributing means for alternately supplying and releasing liquid un-- der pressure to and from, said liquid pressure operated means for controlling the inlet valve or valves of the compressor, said distributing means comprising a rotary valve operative by the crankshaft and having a supply port always communicating with said supply passage and a pressure-relief port always communicating with said chamber, said ports being adapted alternately (to communicate for predetermined intervals with the liquid pressure operated means of each inlet valve in sequence during operation of the compressor. '7

BI IR'I'ON S. AIKMAN. 

